1. Field of the Invention
The present invention relates to an electron emission display and a driving method thereof, and more particularly, which adjust a brightness differently according to a brightness of a frame in order to reduce power consumption and prevent a gradual failure from occurring.
2. Discussion of the Related Art
Lightweight and thin flat panel displays have been used as either a display of a portable information terminal such as a personal computer, a portable telephone, and a Personal Digital Assistance (PDA) or a monitor of all kinds of information devices. A Liquid Crystal Display (LCD) using a liquid crystal panel, an organic light emitting display using Organic Light Emitting Diodes (OLEDs), and a Plasma Display Panel (PDP) using a plasma panel are examples of such a flat panel display.
Flat panel displays are classified as active matrix displays and passive matrix displays according to their construction, and memory drive displays and non-memory drive displays according to their drive method. In general, the active matrix displays can correspond to the memory drive displays, and the passive matrix displays can correspond to the non-memory drive displays. The active matrix displays and memory drive displays emit light in frames. In contrast to this, the passive matrix and non-memory drive displays emit light in lines.
In commonly used flat panel displays, Thin Film Transistor Liquid Crystal Displays (TFT-LCDs) are active matrix displays, and a newly developed Organic Light Emitting Diodes (OLEDs) are also active matrix displays. In contrast to this, an electron emission display is a passive matrix display. Unlike flat panel displays, the electron emission display is a non-memory drive display and uses a line scan that emits light only when a selected line among horizontal lines is selected while sequentially selecting the horizontal lines. That is, the electron emission display drives have a constant duty ratio.
An electron emission display includes a pixel portion, a data driver, a scan driver, a timing controller, and a power supply section.
The pixel portion includes pixels formed at intersecting parts of cathode electrodes and gate electrodes. In the pixels, electrons emitted by the cathode electrodes collide with the anode electrodes to emit light of fluorescent substances, thereby representing a gray scale of an image. The represented gray scale of an image changes according to a value of an input digital image signal. In general, in order to adjust the gray scale expressed according to the value of a digital image signal, a Pulse Width Modulation (PWM) mode or a Pulse Amplitude Modulation (PAM) mode can be used.
The data driver is coupled to the cathode electrodes, and generates and transfers a data signal to the pixel portion, so that the pixel portion emits light corresponding to the data signal.
The scan driver is coupled to the gate electrodes, and generates and transfers a scan signal to the pixel portion. The pixel portion sequentially emits light during a predetermined time period in horizontal line units and in a line scan manner. This causes a total screen to be displayed, thus reducing a cost of the circuits and its power consumption.
The timing controller transfers a data driver control signal and a scan driver control signal to the data driver and the scan driver in order to respectively control operations of the data driver and the scan driver.
The power supply section supplies power to the pixel portion, the data driver, the scan driver, and the timing controller, so that the pixel portion, the data driver, the scan driver, and the timing controller operate.
The electron emission display having the construction mentioned above, expresses a gray scale according to brightness data regardless of total frame data. Consequently, in order to express a higher brightness, a large amount of current flows through the pixel portion. In order to express a lower brightness, a small amount of current flows through the pixel portion. When a large amount of current flows through the pixel portion to express a higher brightness, a large load is applied to the power supply section. This causes a problem in that a high output power supply section is required.
Furthermore, a person's eyes sense brightness changes of a dark image better than that of a bright image. Consequently, the brightness change amount of the dark image must be increased.